Electrolytic looping for forming layering in the deposit of a coating

ABSTRACT

A method for depositing a metal onto a substrate including the steps of providing a plating bath including ions of the metal, positioning the substrate in the plating bath, positioning at least one counter electrode in the plating bath, performing a first electrolytic process for a predetermined first period of time, performing a second electrolytic process for a predetermined second period of time and looping between the first and second electrolytic processes to form a coating of the metal on the substrate.

BACKGROUND

The present disclosure relates to forming layering of a coating and,more particularly, to forming layering of trivalent chromium forequivalent performance characteristics normally associated with ahexavalent chromium coating.

The present disclosure also relates to forming layering in the depositwith disassociated cracks and, more particularly, to forming layering inthe deposit using a looping first electrolytic process followed by asecond electrolytic process and, still more particularly, to forminglayering in the deposit using a looping first electrolytic processfollowed by a second electrolytic process whereby said firstelectrolytic process and said second electrolytic process are separatedby an off-time.

As hexavalent chromium [Cr(VI)] plating continues to be scrutinized forits known human carcinogenicity, a reliable and cost-effectivealternative coating is desirable. One such alternative is trivalentchromium [Cr(III)]. While one skilled in the art believes the use oftrivalent chromium to be limited only to decorative use, the subjectmatter of this disclosure is also applicable for functional use.

Chromium coatings are widely used in a variety of industries. Platingoperations are used to fabricate two types of chromium coatings,functional and decorative. Functional chromium coatings consist of athick layer of chromium, typically 1.3 to 760 μm (F. Altmayer, Plating &Surface Finishing, 82 (2), 26 (1995), to provide a surface withfunctional properties such as hardness, corrosion resistance, wearresistance and low coefficient of friction. Applications of functionalchromium coatings include strut and shock absorber rods, hydrauliccylinders, crankshafts and industrial rolls. Carbon steel, cast iron,stainless steel, copper, aluminum and zinc are substrates commonly usedwith functional chromium. Decorative chromium coatings consist of a thinlayer of chromium, typically 0.003 to 2.5 μm (F. Altmayer, Plating &Surface Finishing, 82 (2), 26 (1995), to provide a bright surface withwear and tarnish resistance when plated over a nickel layer. It is usedfor plating automotive trim/bumpers, bath fixtures and small appliances.

Cr(VI) plating has been commercialized for many years. However, a Cr(VI)plating bath operates at an elevated temperature and produces aproblematic mist of chromic acid. Since worker exposure to Cr(VI)plating baths is regulated by OSHA, exhaust/scrubber systems must beinstalled for Cr(VI) plating operations and the exposure limit is 0.01mg/m (L. R. Ember, Chemical and Engineering News, Feb. 18, 1991) (L.Banker, “Chromium Air Emissions Standards for Hard, Decorative Chromiumand Chromium Anodizing,” Proc. 16th AESF/EPA Conference, Orlando, Fla.,AESF, Washington, D.C., 1995). The Clean Air Act, as well as localconstraints, regulates the emission of chromium to the air and water.Since Cr(VI) plating produces hazardous air emissions, all Cr(VI)platers must control and monitor the bath surface tension and report theresults to the EPA. By contrast, Cr(III) platers are not required tomonitor bath surface tension (L. Banker, “Chromium Air EmissionsStandards for Hard, Decorative Chromium and Chromium Anodizing,” Proc.16th AESF/EPA Conference, Orlando, Fla., AESF, Washington, D.C., 1995).

The USEPA has identified chromium as one of 17 “high-priority” toxicchemicals. The USEPA selected the high-priority chemicals based on theirknown health and environmental effects, production volume and potentialfor exposure (L. R. Ember, Chemical and Engineering News, Feb. 18,1991). Under former USEPA administrator William K. Reilly's IndustrialToxic Program, the high-priority toxic chemicals were targeted for 50%reduction by 1995 (D. J. Hanson, Chemical and Engineering News, Jun. 3,1991).

The chemistry of chromium provides a basis for understanding thetoxicology. Chromium can exist in oxidation states ranging from II toVI. However, only Cr(III) and Cr(VI) are stable enough to actually beused as a basis for electrodeposition. Cr(VI) is readily reduced to themore stable Cr(III) and, in this process, substances in contact withCr(VI) are oxidized. Cr(VI) compounds are very soluble as compared toCr(III) compounds. Therefore, in the environment, Cr(VI), on releaseinto a stream or aquifer, is much more likely to dissolve and move withthe flow. In fact, one method that has been used to stabilize Cr(VI)(i.e., make it less mobile) in the environment is to reduce it toCr(III). The use of Cr(III) in industrial and commercial processes ispreferred over Cr(VI) on the basis of the comparison of theirtoxicities.

From an environmental perspective, plating from additive-free Cr(III)solution has several advantages relative to Cr(VI):

-   -   1. Cr(III) is non-toxic, non-hazardous and is not an oxidizer.        Therefore, meeting air quality regulations is easier and working        conditions are greatly improved. The exposure limit for Cr(III)        is an order of magnitude higher than that for Cr(VI).    -   2. Disposal costs are significantly reduced for Cr(III) plating.        Hydroxide sludge generation is reduced ten to twenty times        because Cr(III) generally operates at a Cr(III) content of about        4 to 20 g/L vs. 150 to 300 g/L for a Cr(VI) bath.    -   3. Since there are no proprietary additives in the Cr(III) bath,        the rinse water may be recycled

In addition, Cr(III) has the following technical advantages:

-   -   1. The Cr(III) plating bath is not sensitive to current        interruptions (G. E. Shahin, Plating & Surface Finishing, 79        (8), 19 (1992).    -   2. Drag-in of chloride and sulfate from any previous nickel        plating operations into the Cr(III) process is tolerated (D. L.        Snyder, Products Finishing, 61 (8), (1989). By contrast,        chloride and sulfate drag-in upset the catalyst balance in a        Cr(VI) process.    -   3. Throwing power for Cr(III) plating, which is poor in a Cr(VI)        bath, is good and similar to other metals such as copper (D. L.        Snyder, Products Finishing, 61 (8), (1989).

As described above, Cr(III) plating has numerous environmental, healthand technical advantages relative to Cr(VI) plating. Considerableresearch has been done to study Cr(III) plating, including the effectsof the plating bath chemistry on plating thickness, brightness, hardnessand corrosion resistance (G. Scott, U.S. Pat. No. 5,196,109 (1991) (M.Constantin, et al., Galvanotechnik, 82 (11), 3819 (1991) (J.-Y. Hwang,Plating & Surface Finishing, 78 (5), 118 (1991) and the effect ofcurrent waveforms on chromium deposit structure, distribution,brightness and hardness (Z.-M. Tu, et al., Plating & Surface Finishing,77 (10), 55 (1990) (J. Dash, et al., Proc. AESF SUR/FIN 1991, AESF,Washington, D.C., 1991; p. 947).

By including proprietary organic additives, Cr(III) plating baths arecommercially available for decorative chromium coating applications.However, the additives are difficult to control because of their lowconcentration. Furthermore, the additives react and breakdown with timeto form contaminants. Due to these contaminants, the used Cr(III) bathand rinse water cannot be replenished and recycled due to the “drag-in”and buildup of these contaminants. Finally, decorative Cr(III) platingstill suffers from low current efficiency.

Currently, functional chromium plating from a Cr(III) bath is notcommercially available because of the difficulty of plating thickchromium coatings with the appropriate properties. In addition, the lowcurrent efficiency and low plating rate of Cr(III) baths lead tounfavorable economics. Due to the rapid drop in current efficiency, thepractical limit for existing conventional DC Cr(III) plating is 2.5 μm(Z.-M. Tu, et al., Plating & Surface Finishing, 80 (11), 79 (1993). Theplating thickness increases quickly at the beginning of theelectroplating process. As plating continues, the deposition ratediminishes and becomes negligible.

During Cr(III) plating, chromium is deposited and hydrogen is evolved atthe cathode, as described by the following reactions:

Cr⁺³+3e ⁻→Cr(φ⁰=−0.74 V_(SHE))  (1)

2H⁺+2e ⁻→H₂(φ⁰=0.0 V_(SHE))  (2)

The current efficiency for chromium plating from a Cr(III) bath isusually below 20%. Therefore, about 80% of the current is used for thehydrogen evolution reaction. As a result, the pH near the cathodesurface increases dramatically and chromic hydroxide (K_(sp)=5.4×10⁻³¹)precipitates in the high pH layer at the cathode. The sedimentation ofchromic hydroxide covers the cathode surface and its thickness increasesas the plating time and pH increase. This promotes an increase ofcathode polarization, a further decrease of chromium plating efficiency(i.e., an increase in the hydrogen evolution reaction), and an increaseof impurities in the plating film. All of these factors retard thenormal growth of crystals in the plating film and lead to the preventionof further plating of chromium. The evolution of hydrogen continues asthe only reaction. The precipitation of chromic hydroxide at the cathodealso results in surface cracks and reduces the hardness and brightnessof the chromium coating. An approach to overcoming the hydrogenevolution problem by utilizing pulsed reverse current plating has beenpreviously described by Tamhaukar et. al. (U.S. Pat. No. 5,242,535 filed29 Sep. 1992) and Taylor (U.S. patent application Ser. No. 08/871,599filed 9 Jun. 1997, now abandoned).

Accordingly, there is a need for a method for producing functionalCr(III) coatings which do not form continuous cracks from the coatingsurface through to the substrate.

SUMMARY

In one aspect, the disclosed method for depositing a metal onto asubstrate includes the steps of providing a plating bath including ionsof the metal, positioning the substrate in the plating bath, positioningat least one counter electrode in the plating bath, performing a firstelectrolytic process for a predetermined first period of time,performing a second electrolytic process for a predetermined secondperiod of time and looping between the first and second electrolyticprocesses to form a coating of the metal on the substrate.

Other aspects of the disclosed method will become apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a commercially available Cr(VI) deposit withoutcontinuous cracks as described in the prior art;

FIG. 2 illustrates a Cr(III) deposit with continuous cracks as describedin the prior art;

FIG. 3A illustrates the beginning stage of a deposit of Cr(III)according to one aspect of the disclosed method;

FIG. 3B illustrates further progression of the deposit of FIG. 3A;

FIG. 3C illustrates further progression of the deposit of FIG. 3B;

FIG. 3D illustrates further progression of the deposit of FIG. 3C; and

FIG. 3E illustrates the final stage of the deposit of FIG. 3D, whereinthe final Cr(III) coating deposit is formed without continuous cracksfrom the coating surface through to the substrate.

The descriptions and identification of the items in the figures aretabulated in the following table:

Numeral Item Description 100 Substrate 200 Coating 200a Initial CoatingLayer 200b Additional Coating Layer 200c Additional Coating Layer 200dFinal Coating Layer 302 Cracks Formed to the Coating Layer Surface 304Cracks Formed Within the Coating Layer 306 Cracks Formed to the CoatingLayer Base 308 Cracks Formed Continuously From the Substrate through theCoating Surface 308a Cracks Formed Continuously From the Substratethrough the Coating Layer Surface 308b Cracks Formed Continuously Fromthe Prior Layer through the Coating Layer Surface 308c Cracks FormedContinuously From the Prior Layer through the Coating Layer Surface 308dCracks Formed Continuously From the Prior Layer through the CoatingLayer Surface

DETAILED DESCRIPTION

The present disclosure provides a method for achieving a functionalCr(III) coating with minimal or reduced disassociated cracks. TheCr(III) coating is produced by forming layering in the deposit using alooping first electrolytic process followed by a second electrolyticprocess whereby said first electrolytic process and said secondelectrolytic process may be separated by an off-time to formdisassociated cracks in the coating. The first electrolytic process maybe either a direct current process, a pulse current process or a pulsereverse current process. The second electrolytic process may be either adirect current process, a pulse current process or a pulse reversecurrent process. The pulse current process and pulse reverse currentprocesses are described in U.S. Pat. No. 6,203,684 to Taylor, the entirecontents of which are incorporated herein by reference.

The resulting coating is built up from a series of layers. This layeringstructure enables interruption to crack propagation to reduce thelikelihood of crack propagation from the substrate through the outercoating layer surface. The greater the number of layering used to formthe coating the less likely the number of cracks propagating from thesubstrate to the outer surface of the coating. One skilled in the artmay adjust the timing of the first electrolytic process and the secondelectrolytic process to obtain an acceptable level of cracks propagatingfrom the substrate to the surface of the coating without undoexperimentation.

FIG. 1 illustrates a commercially available Cr(VI) deposit withoutcontinuous cracks as described in the prior art. The coating (200) builtup from the substrate (100) has desirable crack formation includingthose residing from the coating through the coating surface (302), thoseresiding within the coating (304), and those residing from the substrate(100) into the coating (306).

FIG. 2 illustrates a Cr(III) deposit with continuous cracks as describedin the prior art. The coating (200) built up from the substrate (100)has desirable crack formation including those residing from the coatingthrough the coating surface (302), those residing within the coating(304), and those residing from the substrate into the coating (306).Additionally, undesirable cracks (308) residing from the substrate (100)through the coating surface are also present.

FIG. 3A illustrates the beginning stage of the deposition methodaccording to an aspect of the present disclosure, wherein a layer ofCr(III) is deposited. The initial layer (200 a) of the coating (200)built up from the substrate (100) may have desirable crack formationincluding those cracks (302) residing from the layer (200 a) through thelayer (200 a) surface, those cracks (304) residing within the layer (200a), and those cracks (306) residing from the substrate (100) into thelayer (200 a). Additionally, cracks (308 a) residing from the substrate(100) through the layer surface (200 a) may be present.

FIG. 3B illustrates further progression of the deposition of Cr(III),wherein a second layer of Cr(III) is deposited. An additional layer (200b) of the coating (200) built up from the initial layer (200 a) may havedesirable crack formation including those cracks (302) residing from thelayer (200 b) through the layer (200 b) surface, those cracks (304)residing within the layer (200 b), and those cracks (306) residing fromthe layer (200 a) into the layer (200 b). Additionally, cracks (308 b)residing from the layer (200 a) through the layer surface (200 b) may bepresent.

FIG. 3C illustrates further progression of the deposition of Cr(III),wherein a layer of Cr(III) is deposited. An additional layer (200 c) ofthe coating (200) built up from the prior layer (200 b) built up fromthe initial layer (200 a) has desirable crack formation including thosecracks (302) residing from the layer (200 c) through the layer (200 c)surface, those cracks (304) residing within the layer (200 c), and thosecracks (306) residing from the layer (200 b) into the layer (200 c).Additionally, cracks (308 c) residing from the layer (200 b) through thelayer surface (200 c) may be present.

FIG. 3D illustrates further progression of the deposition of Cr(III),wherein a layer of Cr(III) is deposited. An additional layer (200 d) ofthe coating (200) built up from the prior layer (200 c) built up fromthe prior layer (200 b) built up from the initial layer (200 a) hasdesirable crack (302) formation including those residing from the layer(200 d) through the layer (200 d) surface, those cracks (304) residingwithin the layer (200 d), and those cracks (306) residing from the layer(200 c) into the layer (200 d). Additionally, cracks (308 d) residingfrom the layer (200 c) through the layer surface (200 d) may be present.

FIG. 3E illustrates the final stage of the deposition of Cr(III),wherein the final Cr(III) coating (200) deposit is formed withoutcontinuous cracks (308) from the substrate (100) through the coating(200) surface. Desirable crack formation including those cracks (302)residing from the coating (200) through the coating (200) surface, thosecracks (304) residing within the coating (200), and those cracks (306)residing from the substrate (100) into the coating (200) are present.

The disclosed method will be illustrated by the following examples,which are intended to be illustrative only and not limiting.

EXAMPLE 1 Comparative

This example illustrates the use of the electric field consisting onlyof a first electrolytic process with Average current (I_(ave)) of 6.08amps, forward time of 9.00 ms, Cathodic on-time (T_(c)) of 9.00 ms,Reverse time of 1.00 ms, Anodic on-time (T_(a)) of 0.30 ms, Anodicoff-time (T_(off)) of 0.70 ms, Peak cathodic current (I_(c)) of 6.99amps, and Peak anodic current (I_(a)) of 6.99 amps. Total plating timewas 180 min.

This example was plated using a 30 L plating bath prepared as follows:

-   -   1. Heat 15 liters of DI water to about 71° C. (160° F.).    -   2. Add 490 g of Cr₂(SO₄)3·8.5H₂O from Elementis Chromium in        small increments.    -   3. Continue stirring and heating and add 300 g of (NH₄)₂SO4 to        the bath in small increments.    -   4. Continue stirring and heating and add 63 g of H₃BO₃ to the        bath in small increments.    -   5. Continue stirring and heating and add 180 mL of HCOOH to the        bath. PH 1.6.    -   6. Cool below 50° C. and adjust the pH to 2.5 with KOH. 95 g of        KOH used.    -   7. Continue stirring and add DI water to a volume of 3 liters.    -   8. Add 1.2 g of dodecyl sodium sulfate as a surfactant.    -   9. To electrolyze the solution (produce Cr²⁺), add 0.7 g CrCl².

The coating was plated onto a rod having a diameter of about ⅜ inch and,under magnification, the coating exhibited about 280 cracks formedcontinuously from the substrate through the coating surface. Therefore,calculating a coating circumference of about 2.99 cm based upon the roddiameter, the coating was observed to have about 94 continuous cracksper centimeter.

EXAMPLE 2

This example illustrates the use of the looping electric fieldconsisting of a first electrolytic process for 7 min with Averagecurrent (I_(ave)) of 4.64 amps, forward time of 9.00 ms, Cathodicon-time (T_(c)) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time(T_(a)) of 0.30 ms, Anodic off-time (T_(off)) of 0.70 ms, Peak cathodiccurrent (I_(c)) of 5.33 amps, and Peak anodic current (I_(a)) of 5.33amps. The first electrolytic process followed by a second electrolyticprocess was followed by a direct current of 5.00 amps for 3.00 min.Total plating time was 120 min.

This example was plated using a 30 L plating bath prepared as follows:

-   -   1. Heat 15 liters of DI water to about 71° C. (160° F.).    -   2. Add 4900 g of Cr₂(SO₄)3·8.5H₂O from Elementis Chromium in        small increments.    -   3. Continue stirring and heating and add 3000 g of (NH₄)₂SO4 to        the bath in small increments.    -   4. Continue stirring and heating and add 630 g of H₃BO₃ to the        bath in small increments.    -   5. Continue stirring and heating and add 1800 mL of HCOOH to the        bath. PH 1.68.    -   6. Cool below 50° C. and adjust the pH to 2.5 with KOH. 870 g of        KOH used.    -   7. Continue stirring and add DI water to a volume of 30 liters.    -   8. Add 12.0 g of dodecyl sodium sulfate as a surfactant.    -   9. To electrolyze the solution (produce Cr²⁺), add 7.0 g CrCl².

The coating was plated onto a rod having a diameter of about ⅜ inch and,under magnification similar to EXAMPLE 1, the coating exhibited about 50cracks formed continuously from the substrate through the coatingsurface. Therefore, calculating a coating circumference of about 2.99 cmbased upon the rod diameter, the coating was observed to have about 17continuous cracks per centimeter.

EXAMPLE 3

This example illustrates use of the looping electric field consisting ofa first electrolytic process for use of the looping electric fieldconsisting of a first electrolytic process 9 min with Average current(I_(ave)) of 4.64 amps, forward time of 9.00 ms, Cathodic on-time(T_(c)) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time (T_(a)) of0.30 ms, Anodic off-time (T_(off)) of 0.70 ms, Peak cathodic current(I_(c)) of 5.33 amps, and Peak anodic current (I_(a)) of 5.33 amps. Thefirst electrolytic process followed by a second electrolytic process wasfollowed by a direct current of 5.00 amps for 3.00 min. Total platingtime was 120 min.

This example was plated using the same plating bath described in EXAMPLE2. The coating was plated onto a rod having a diameter of about ⅜ inchand, under magnification similar to EXAMPLE 1, the coating exhibitedabout 84 cracks formed continuously from the substrate through thecoating surface. Therefore, calculating a coating circumference of about2.99 cm based upon the rod diameter, the coating was observed to haveabout 28 continuous cracks per centimeter.

EXAMPLE 4

This example illustrates the use of the looping electric fieldconsisting of a first electrolytic process for 9 min with Averagecurrent (I_(ave)) of 4.64 amps, forward time of 9.00 ms, Cathodicon-time (T_(c)) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time(T_(a)) of 0.30 ms, Anodic off-time (T_(off)) of 0.70 ms, Peak cathodiccurrent (I_(c)) of 5.33 amps, and Peak anodic current (I_(a)) of 5.33amps. The first electrolytic process followed by a second electrolyticprocess was followed by a direct current of 5.00 amps for 1.00 min.Total plating time was 120 min.

This example was plated using the same plating bath described in EXAMPLE2. The coating was plated onto a rod having a diameter of about 3/8 inchand, under magnification similar to EXAMPLE 1, the coating exhibitedabout 89 cracks formed continuously from the substrate through thecoating surface. Therefore, calculating a coating circumference of about2.99 cm based upon the rod diameter, the coating was observed to haveabout 30 continuous cracks per centimeter.

EXAMPLE 5

This example illustrates the use of the looping electric fieldconsisting of a first electrolytic process for 3 min with Averagecurrent (I_(ave)) of 4.64 amps, forward time of 9.00 ms, Cathodicon-time (T_(c)) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time(T_(a)) of 0.30 ms, Anodic off-time (T_(off)) of 0.70 ms, Peak cathodiccurrent (I_(c)) of 5.33 amps, and Peak anodic current (I_(a)) of 5.33amps. The first electrolytic process followed by a second electrolyticprocess was followed by a direct current of 5.00 amps for 1.00 min.Total plating time was 120 min.

This example was plated using the same plating bath described in EXAMPLE2. The coating was plated onto a rod having a diameter of about ⅜ inchand, under magnification similar to EXAMPLE 1, the coating exhibitedabout 74 cracks formed continuously from the substrate through thecoating surface. Therefore, calculating a coating circumference of about2.99 cm based upon the rod diameter, the coating was observed to haveabout 25 continuous cracks per centimeter.

EXAMPLE 6

This example illustrates the use of the looping electric fieldconsisting of a first electrolytic process for 2.5 min with Averagecurrent (I_(ave)) of 4.64 amps, forward time of 9.00 ms, Cathodicon-time (T_(c)) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time(T_(a)) of 0.30 ms, Anodic off-time (T_(off)) of 0.70 ms, Peak cathodiccurrent (I_(c)) of 5.33 amps, and Peak anodic current (I_(a)) of 5.33amps. The first electrolytic process followed by a second electrolyticprocess was followed by a direct current of 5.00 amps for 0.5 min. Totalplating time was 120 min.

This example was plated using the same plating bath described in EXAMPLE2. The coating was plated onto a rod having a diameter of about ⅜ inchand, under magnification similar to EXAMPLE 1, the coating exhibitedabout 68 cracks formed continuously from the substrate through thecoating surface. Therefore, calculating a coating circumference of about2.99 cm based upon the rod diameter, the coating was observed to haveabout 23 continuous cracks per centimeter.

All documents cited herein are, in relevant part, incorporated herein byreference; the citation of any document is not to be construed as anadmission that it is prior art with respect to the present invention.

Although various aspects of the disclosed method have been shown anddescribed, modifications may occur to those skilled in the art uponreading the specification. The present application includes suchmodifications and is limited only by the scope of the claims.

1. A method for depositing a metal onto a substrate comprising the stepsof: providing a plating bath including ions of said metal; positioningsaid substrate in said plating bath; positioning at least one counterelectrode in said plating bath; performing a first electrolytic processfor a predetermined first period of time; performing a secondelectrolytic process for a predetermined second period of time; andlooping between said first electrolytic process and said secondelectrolytic process to form a coating of said metal on said substrate.2. The method of claim 1 wherein said metal is chromium.
 3. The methodof claim 1 wherein said ions of said metal are chromium(III) ions. 4.The method of claim 1 wherein said first electrolytic process is adirect current process.
 5. The method of claim 1 wherein said firstelectrolytic process is a pulse current process.
 6. The method of claim1 wherein said first electrolytic process is a pulse reverse currentprocess.
 7. The method of claim 1 wherein said second electrolyticprocess is a direct current process.
 8. The method of claim 1 whereinsaid second electrolytic process is a pulse current process.
 9. Themethod of claim 1 wherein said second electrolytic process is a pulsereverse current process.
 10. The method of claim 1 wherein said coatinghas less than 50 cracks per centimeter formed continuously through saidcoating.
 11. The method of claim 1 wherein said first electrolyticprocess is a direct current process and said second electrolytic processis at least one of a pulse current process and a pulse reverse currentprocess.
 12. The method of claim 1 wherein said first electrolyticprocess is a pulse current process and said second electrolytic processis at least one of a direct current process and a pulse reverse currentprocess.
 13. The method of claim 1 wherein said first electrolyticprocess is a pulse reverse current process and said second electrolyticprocess is at least one of a direct current process and a pulse currentprocess.
 14. The method of claim 1 wherein said first electrolyticprocess and said second electrolytic process are the same electrolyticprocess and said first electrolytic process and said second electrolyticprocess are separated by a predetermined off-time.
 15. The method ofclaim 1 wherein said coating has a thickness of about 1 to about 100mils.
 16. The method of claim 1 wherein each of said first and secondelectrolytic processes deposits a layer of said metal.